Under some circumstances it would be advantageous to take the pressurized air from the compressor section of a gas turbine engine and cause this pressurized air to pass in heat exchange with the hot exhaust gases of the engine, before the pressurized air from the compressor section is introduced into the combustor. The heat exchanger, generally referred to as a recuperator, could have a bypass system so that the engine exhaust gasses can, in part at least, bypass the heat exchanger, when desired. One known recuperator with a gas-side bypass is that designed by Solar Turbines Inc. for the M-1 battle tank engine. Recuperated gas turbine engines would be useful, for example, on board a ship. The recuperator would normally be located at the juncture of the gas turbine engine exhaust gas box and the exhaust stack. Such a recuperator would typically comprise a pair of heat exchangers in parallel spaced relationship, the space therebetween defining a bypass duct which is closable by a butterfly valve.
Recuperated engines should achieve excellent low power specific fuel consumption. A major problem arises, however, with respect to the ability to generate high power output during emergency operations or high ship speeds. A major reason for this is the gas-side total pressure losses of the hot exhaust gas stream are high through the exhaust system recuperator. The problem is magnified by the fact that, for installation purposes, the size of the recuperator is desired to be as small as possible. A related problem results from the fact that, with the desire for a smaller recuperator, less space would be available for a bypass system. As a result of all this, under high-flow, high-power conditions, high exhaust total pressure losses would be experienced.
The present invention is based upon the discovery that if the longitudinal edges of the bypass duct are provided with the flow divider devices of the present invention, as described hereinafter, the effective area of a rectangular bypass duct may be increased as much as from about thirty percent (30%) to forty percent (40%). This allows nearly a one-hundred percent (100%) bypass of the recuperator heat exchangers. The maximum shaft horsepower capability is increased by about twelve percent (12%). The invention enables a minimum sized duct between the recuperator heat exchangers because the rectangular duct flow coefficient is improved from about 0.60-0.70 to about 0.99. This, in turn, saves weight, space and cost.